Process for the manufacture of particle boards utilizing a dry organic binder

ABSTRACT

A PROCESS FOR THE MANUFACTURE OF BOARDS CONSISTING OF AT LEAST ONE LAYER, WHEREIN SAWDUST HAVING A PARTICLE SIZE BELOW 1 MM. IS MIXED WITH A QUANTITY OF BINDING AGENT RANGING BETWEEN 5% AND 15% OF THE WEIGHT OF THE DRY SAWDUST, AND A LAYER IS FORMED BY SPREADING THE MIXTURE IN A LAYER OF SUCH A THICKNESS THAT A FINAL LAYER OF A THICKNESS RANGING BETWEEN 0.5 MM. AND 5 MM. IS OBTAINED, AND BY SIMULTANEOUSLY APPLYING A PRESSURE RANGING BETWEEN 80 KG./CM.2 AND 150 KG/CM2 AT A TEMPERATURE RANGING BETWEEN 130*C. AND 180*C. A PROCESS IN WHICH AN AGENT INCREASING THE INTERNAL HEAT RESISTANCE IS ADDED TO SAID MIXTURE.

United States Patent Int. or. 13291 5/00 US. Cl. 15662.2 13 Claims ABSTRACT OF THE DISCLOSURE A process for the manufacture of boards consisting of at least one layer, wherein sawdust having a particle size below 1 mm. is mixed with a quantity of binding agent ranging between 5% and 15% of the Weight of the dry sawdust, and a layer is formed by spreading the mixture in a layer of such a thickness that a final layer of a thickness ranging between 0.5 mm. and 5 mm. is obtained, and by simultaneously applying a pressure ranging between 80 kg/cm. and 150 kg./c1n. at a temperature ranging between 130 C. and 180 C.

A process in which an agent increasing the internal heat resistance is added to said mixture.

The present invention relates to a process for the manufacture of boards, in which sawdust is mixed with a binding agent and the mixture is subjected to a pressure at an elevated temperature.

A process for the manufacture of boards of this type has already been proposed, in which sawdust having a particle size ranging between 2 mm. and 9 mm. is used and mixed with a quantity of thermosetting binding agent, ranging between 7% and 10% of the weight of dry resin, this mixture then being subjected to a pressure ranging between 25 kg./cm. and 35 kg./cm. at a temperature ranging between 130 C. and 140 C.

The boards obtained according to this process have characteristics of bending, water-absorption and swelling, which makes them unsuitable for use as covering panels of very low thickness, i.e. of 0.5 mm. to 5 mm.

The present invention has for its object a process for the manufacture of boards of very low thickness from a mixture of sawdust and a binding agent, which has mechanical properties similar to those hitherto obtained by ply boards formed from [live to six superimposed sheets of paper, which are impregnated with a phenolic binding agent and compressed under pressure at elevated temperature.

In the process according to the invention, the mixture is effected with sawdust having a particle size below 1 mm. and with a quantity of binding agent ranging between 5% and of the weight of the dry dust; said layer is formed by spreading the mixture in a layer of such a thickness that a final layer of a thickness ranging between 0.5 mm. and 5 mm. is obtained, and by simultaneously applying a pressure ranging between 80 kg/cm? and 150 kg./cm. and a temperature ranging between 130 C. and 180 C.

According to one feature of the process, sawdust is used which has a moisture content of 5% to 15 According to another feature mixing is performed with a thermosetting binding agent.

The binding agent is advantageously a phenolic resin.

According to another feature, the binding agent is an abietic resin.

According to another feature the binding agent contains lignin.

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The binding agent advantageously contains several resins chosen from among the resins of the phenolic, fossil, natural type and lignin type.

According to yet another feature the mixture contains an agent increasing the internal resistance to heat of the boards formed. This agent advantageously consists of five parts by weight of cement or plaster calculated on the mixture.

According to another feature of the process, a layer of the mixture of sawdust and binding agent is applied to a supporting sheet consisting of a cellulosic material, for example paper impregnated with phenolic resin.

In a variant the support consists of a synthetic plastics material such as a polyvinyl or polyolefin.

In another variant of the invention, the mixture of sawdust and binding agent is subjected to a cold precompression at a pressure ranging between 10 kg./cm. and 40 kg./cm. This precompression permits the production of a cake facilitating the subsequent application of a cover paper prior to the hot compression. This cover sheet consists of a cellulosic material impregnated with a synthetic plastic resin, such as polyester, acrylic, epoxy, or of a film of plastics material produced with the above-stated materials. This cover forms advantageously a support for ornamental elements.

Other features and details of the invention will become apparent from the description of the following examples:

EXAMPLE 1 Continuous manufacture of a finished board of 1.5 mm. thickness A mixture is prepared comprising parts by weight of sawdust of a particle size below 1 mm. and having a moisture content of about 8.5% and 10 dry parts of a phenolic resin in the dry state. The composition, whose pH is 7.5 is homogenised. The mixture is spread onto a phenolised sheet of kraft paper conveyed on a continuously rotating conveyor belt. This sheet is intended to form the back of the adhesive surface of the board. The layer of mixture is spread in a uniform manner to a thickness of about 8.5 mm. by means of a rotary brush which rotates in the direction opposite to that of the forward motion of the board in formation. A cover sheet such as an ornamental paper impregnated with melamine resin is applied to the layer thus formed, and a glossy or matt according to the final aspect desired-metal sheet is applied to the latter. The whole is inserted between two platescooled to approximately 40 C.of a press, The press is slowly closed to allow the air to be evacuated and a pressure of kg./cm. is applied for 5 minutes to the layer of material, the plates of the press being heated to about C. The plates are cooled by circulating cold water and when the internal temperature has dropped to 50 C. the press is opened.

The board obtained has a thickness of 1.5' mm. and a density of 1.35 g./cm. The resistance to bending by compression of the decorated surface is 800 kg./cm. to 900 kg./cm. The increase of volume after standing in water at 100 C. for 2 hours is 4.5% whilst the increase of weight is 5%.

EXAMPLE 2 Manufacture of a finished panel of 3 mm. thickness decorated on both faces A mixture is prepared comprising:

85 parts of sawdust of a particle size below 0.5 mm. and

having a moisture content of 9%,

5 parts of Portland cement,

5 parts of powdered phenolic resin,

5 parts of powdered lignin.

The mixture which has a pH of about 8.5 is homogenised. A 19 mm. layer of the mixture is spread onto a supporting paper impregnated with phenolic resin and conveyed on a conveyor belt. The whole is subjected to a precompression of 30 -kg./cm. at ambient temperature. The cake provided with its support is then placed on a metal sheet covered by a decorated, melamine-impregnated paper and to the upper face of the cake are successively applied: a supporting paper impregnated with a phenolic resin, a decorated paper impregnated with a melamine resin and a metal sheet.

The upper and lower metal sheets are polished, matt or grainted according to the final aspect desired.

The whole is introduced between two plates of a press cooled to 40 C. and then compressed for -8 minutes at 100 kg/cm. at a temperature of 150 C. The plates are cooled to less than 50 C. and the pressure is relaxed. A very rigid board of a thickness of 3 mm., having a density of 1.40 g./cm. and a very low water absorbing power is obtained. The resistance to bending by compression is 700 to 800 kg./cm. The increase of volume after standing in water for two hours at 100 C. is 3.5% and the weight increase 4%.

EXAMPLE 3 The present invention likewise allows one to obtain boards of a greater thickness of about 20 mm. as will be described in the present example.

This board has a central layer having sawdust of a particle size above 1 mm., for example below 2 mm., and on either side thereof an outer layer comprising sawdust of a particle size below 1 mm., for example below 0.5 mm.

For this purpose two mixtures of sawdust of different particle sizes are prepared, for example one of less than 0.5 mm. and the other less than 2 mm. These mixtures comprise:

85 parts of sawdust having 8.5% of moisture, 5 parts of plaster,

5 parts of abietic resin,

5 parts of phenolic resin.

The mixtures are homogenised. A first layer of a thickness of 8.5 mm. containing the sawdust having a particle size below 0.5 mm. is distributed over a rigid polyvinyl chloride sheet of a thickness of 0.3 mm. Over this layer is distributed a second layer of a thickness of 118 mm. of the mixture containing sawdust having a particle size below 2 mm., and a third layer identical with the first is spread thereon. The whole is subjected to cold precompression at a pressure of 40 kg./cm. and the cake thus obtained is placed onto a metal sheet. An identical rigid polyvinyl chloride and a metal sheet are applied to the surface. The two metal sheets are glossy, matt or grained, according to the final aspect which one desires to obtain. The assembly is introduced into the plates of a press cooled to 40 C. and pressed for 16 minutes at 100 =kg./cm.-- at a temperature of 165 C. The plates are cooled and the pressure is relaxed. The board obtained has a thickness of 20 mm. The bending strength is 650 kg./cm. The increase of volume after standing for 2 hours at 100 C. is 1.7% and the weight increase 15%.

The binding agent is of thermoplastic nature, such as artificial resin e.g. polyvinyl chloride or natural products, such as abietic resin, designated Vinsol or also an asphalt or a fossil resin such as gilsonite, or else lignin, for example extracted from the residual washing solutions of paper pulp factories.

In a variant the binding agent is of thermosetting nature, such as a phenolic formaldehyde resin or one based on furfural.

It is obvious that the invention is not limited to the above examples and that numerous modifications of 4 quantities, concentrations, temperatures, pressures and pH can be introduced at the condition that these modifications are not in contradiction with the object of each of the following claims.

What I claim is:

1. A process for manufacturing panels having at least one layer of a thickness of from 0.5 to 5 mm. consisting essentially of:

forming a mixture of sawdust having a particle size of below 1 mm. and a moisture content of from 5 to 15% with from 5 to 15 weight percent, based on the weight of the dry sawdust, of a dry organic binding agent; and

spreading said mixture into a layer having a thickness such that the final layer has a thickness of from 0.5 to 5 mm. and simultaneously subjecting said layer to a pressure of from to kg./cm. at a temperature of from 130 to C.

2. The process of claim 1 wherein, prior to subjecting saidlayer to said pressure, a second layer is formed over the resulting first layer, said second layer comprising a mixture of sawdust having a particle size of above 1 mm. and a dry organic binding agent.

3. The process of claim 2 wherein, prior to subjecting both of the resulting layers to said pressure, a third layer is formed over said second layer, said third layer comprising a mixture identical to that employed for the first layer.

4. The process of claim 1 wherein the internal resistance to heat of said mixture is increased by adding thereto at least one member selected from the group consisting of cement and plaster.

5. The process of claim 1 wherein, prior to subjecting said layer to said pressure, said layer is applied to a supporting sheet.

6. The process of claim 1 wherein, prior to subjecting said layer to said pressure, a cover sheet is applied to said ayer.

7. The process of claim 1 wherein, prior to subjecting said layer to said pressure, at said temperature, said layer is subjected to a cold pre-compression at a pressure of from 10 to 40 kg./cm.

8. The process of claim 1 wherein said organic binding agent is a phenolic resin, an abietic resin or lignin.

9. The process of claim 5 wherein said supporting sheet comprises a cellulosic material or a synthetic resin.

10. The process of claim 9 wherein said cellulosic material is paper impregnated with a phenolic resin and wherein said synthetic resin is a polyolefin.

11. The process of claim 4 wherein said cement or said plaster is present in said layer in an amount of about 5 parts by weight, based on the weight of said mixture.

12. The process of claim 6 wherein said cover sheet is a cellulosic material impregnated with a synthetic resin selected from the group consisting of polyesters, acrylics and epoxies.

13. The process of claim 6 wherein said cover sheet is a film of a synthetic resin selected from a group consisting of polyesters, acrylics and epoxies.

References Cited UNITED STATES PATENTS 2,033,411 3/1936 Carson 1847.5 2,200,650 5/1940 Welch 154--2 2,230,880 2/1941 Brown 25l 2,601,349 6/1952 Welch 156276 CARL D. QQUARFORTH, Primary Examiner P. A. NELSON, Assistant Examiner US. Cl. X.R. 

